1. Field of the Invention
The present invention relates to a power supplying apparatus and power supplying method for supplying power to a motor that drives a mechanism, such as a disk auto-changer in a library apparatus.
2. Description of the Related Art
Library apparatuses including a mechanism that conveys storage medium cartridges have been commonly used. I the library apparatus, the storage medium cartridges, such as electromagnetic tapes, electromagnetic disks, optical disks and magneto-optical disks, are stored in a rack. The mechanism conveys the storage medium cartridges between the rack and a drive device that performs reading/writing of data in the storage medium.
When a position to store a cartridge in the rack is designated, the mechanism moves according to a predetermined movement pattern, and an electric current is supplied to a motor that drives the mechanism according to the movement pattern.
FIG. 4 is a schematic for illustrating a relation between movement of the mechanism and the electric current flowing into the motor. When the mechanism conveys a cartridge from the rack to the drive device, or from the drive device to the rack, a state of the mechanism transitionally changes from a stop state, an accelerating state, a constant-speed state, a decelerating state, and back to the stop state.
In the accelerating state, the motor requires a stable supply of electric current to accelerate movement of the mechanism at a fixed rate.
In the decelerating state, if the motor is operated as a power unit, mechanical energy is converted into electric energy. Thus, theoretically, the same amount of electric current as an amount of the electric current input to the motor is generated as a regenerative current. However, practically, the amount of the regenerative current is not the same as the amount of the electric current input to the motor due to an energy conversion loss.
In conventional library apparatuses, the regenerative current is converted into heat to be disposed. FIG. 5 is a block diagram of a conventional power supply system, and FIG. 6 is a block diagram of a conventional power supply system that includes an uninterruptible power supply (UPS).
The power supply system shown in FIG. 5 includes an alternating-current (AC) power source 1 and a library apparatus 2. The AC power source 1 supplies power to the library apparatus 2 at a voltage of 100 volts (V) to 220 V. The library apparatus 2 has the same configuration as described above.
The library apparatus 2 includes a power source 3, a driving-power amplification circuit 4, a commutator 5, a control circuit 6, a motor 7, and a resistance 8.
The power source 3 receives power from the AC power source 1, and supplies the power to the driving-power amplification circuit 4. The driving-power amplification circuit 4 amplifies the power supplied from the power source 3.
The commutator 5 changes a direction of the current to change a direction of rotation of the motor 7. The control circuit 6 controls the commutator 5 to make the direction of the current change.
The motor 7 drives a mechanism (not shown) in the library apparatus 2. A regenerative current is generated in the motor 7 while the mechanism is moving in the decelerating state. The resistance 8 converts the regenerative current into heat to be disposed.
The system shown in FIG. 6 further includes a UPS 9. The UPS 9 is an uninterruptible power supply unit including a lead accumulator that accumulates power. Therefore, even when there is a momentary power failure in the AC power source 1, the power accumulated in the lead accumulator is supplied to the library apparatus 2, so that the library apparatus 2 does not stop operating.
However, in these power supply systems, the regenerative current generated in the motor 7 is wasted to be disposed as heat without being used. Moreover, cost of the power supply system increases if the UPS 9 is provided to counter momentary power failures.
A technology for using the regenerative current and countering momentary power failures is disclosed in, for example, Japanese Patent Application Laid Open No. H7-99740. In the technology, a power unit includes a first capacitor with large capacitance and high anode resistance, a second capacitor with relatively small capacitance and low anode resistance, and a direct current (DC)-DC converter that connects the first capacitor and the second capacitor.
In this power unit, when power is supplied to the first capacitor from an external power unit, the power is supplied to the second capacitor through the DC—DC converter, and then to a load connected to the second capacitor.
Furthermore, when regenerative power generated in the load is supplied to the second capacitor, the DC—DC converter supplies the power to the first capacitor. When the voltage of the second capacitor decreases due to power consumption by the load, the DC—DC converter supplies the power to the second capacitor, and the power is supplied to the load.
However, when the mechanism continuously repeats conveyance of storage medium cartridges for many times, a speed at which the motor consumes power exceeds a speed at which power is accumulated in the first capacitor from the external power unit. Thus, the first capacitor cannot supply enough power to the second capacitor before the power runs out.
Theoretically, the same amount of power consumed by the motor can be obtained by using the regenerative power, however, the same amount of power cannot be obtained by the regenerative power due to the energy conversion loss. As a result, the motor requires power from the external power unit.
Therefore, it is imperative to develop a power supply system that uses regenerative power to reduce power consumption and that supplies a stable amount of power even when power consumption is large.